A Brazilian Army soldier patrols outside the Rio Centro where the "Rio +20" United Nations Conference on Sustainable Development will be held in Rio de Janeiro June 12, 2012. Reuters/ Ricardo Moraes

The message couldn’t have been clearer. The activists were shot, execution style, on the same day in May 2011 that Brazil’s Chamber of Deputies passed a rewrite of the Forest Code, the law governing economic activity in the Amazon. Zé Cláudio Ribeiro da Silva and Maria do Espírito Santo, a married activist couple, were gunned down near their forest home in Pará, in northeastern Brazil. They were the latest of the more than 1,600 activists who have been killed in the Amazon since 1985, including Chico Mendes, the rubber-tapper and political organizer whose 1988 assassination drew worldwide condemnation.

Like Mendes, Ribeiro had received numerous death threats and predicted his own murder. In November 2010 the forest defender told an audience in Manaus, “I could get a bullet in my head at any moment…because I denounce the loggers.” Police immediately suspected that Ribeiro’s death was a professional hit, because his corpse, like his wife’s, had one ear cut off; in the Amazon, killers customarily present their paymasters with a victim’s ear to prove the deed was done. Hours later, when a legislator took the floor in the Brazilian Chamber of Deputies to urge an investigation, he was booed by members of the ruralista caucus, lawmakers allied with the large landowners who advocate maximum exploitation of the Amazon.

An ominous sense of déjà vu hovers over the United Nations Rio+20 conference on sustainable development taking place June 20–22. Twenty years ago, Rio de Janeiro hosted the landmark 1992 Earth Summit, which framed the problem that Rio+20 re-examines: how to reduce global poverty while preserving the planet’s life-support systems. Alas, two decades later, the Amazon remains a lawless place, where criminals loot natural resources with abandon and violent intimidation of activists is common. (A current example is forest defender Nilcilene Miguel de Lima, who, as reported by Brazil’s Publica news group, got so many death threats the government gave her twenty-four-hour security protection, then moved her to an undisclosed location.)

Internationally, too, the parallels between Rio+20 and the Earth Summit are disturbing. Like George H.W. Bush in 1992, President Obama refused to say for weeks whether he would attend the Rio conference, much less try to rally the world to avert planetary catastrophe. On June 12 a State Department announcement made it official: Obama will not go. When Bush was trying to duck the summit in 1992, major media outlets ran a slew of stories reminding him of the potential impact on his re-election efforts, which helped change his mind. Obama has faced no such flak for being a Rio no-show.

Why should he? After all, Rio+20 is only talking about the end of the world as we know it. A new study in the journal Nature warns that Earth is approaching a “tipping point” that could lead, within decades, to irreversible degradation of the natural systems that provide humans with food, water and other vital services. A team led by Anthony Barnosky of the University of California, Berkeley, found that the rapidly warming climate, the disappearance of countless plant and animal species, the spread of toxic “dead zones” in the oceans, and other disturbing trends could trigger a transition to a radically less hospitable planet that would be “extremely difficult or even impossible” to reverse.

Yet it’s no mystery how to tackle these problems, either in Brazil or globally. The rate of deforestation in the Amazon has actually been falling, making Brazil the world’s leader in reducing greenhouse gas emissions. According to satellite imagery from Brazil’s space agency, “Between 2006 and 2010, Brazil reduced Amazon deforestation about two-thirds below the annual average from 1996 to 2005, reducing about 1 billion tons of greenhouse gas pollution,” writes Steve Schwartzman, who as director of tropical forest policy for the Environmental Defense Fund has worked in the Amazon for decades. He credits tougher law enforcement initiated under Marina Silva, the former environment minister (and an activist ally of Mendes before entering government). Tatiana Carvalho of Greenpeace Brazil cites another reason: a Greenpeace campaign that persuaded global companies not to buy soy from Amazon clear-cutters.

However, in response to tougher law enforcement, the ruralistas set out to gut the Forest Code, says Schwartzman. The rewritten code increased the number of trees that could be cut and granted amnesty for previous deforestation. President Dilma Rousseff had promised to oppose such an amnesty, and Brazil’s leading scientific organizations and many others urged her to veto the rewritten code. Nevertheless, on May 25—a year and a day since the murders of Ribeiro and Santo—Rousseff issued only a “partial veto,” which activists decry as a giant step backward: it retained amnesty for illegal deforestation if it occurred before 2008 on land holdings up to 1,000 acres. The Brazilian embassy in Washington did not respond to repeated requests for comment.

Brazil is hardly the only culprit: money and power often trump sensible policy around the world. Under current rules, polluters in many countries can emit greenhouse gases for free; they are even subsidized with hundreds of billions of tax dollars. Likewise, perhaps the most powerful step toward reducing poverty would be for the United States and other wealthy nations to slash the subsidies to domestic agriculture that undercut poor farmers’ ability to compete in world markets. Northern governments sometimes rhetorically endorse such reforms—Group of 20 leaders pledged in 2009 to phase out fossil fuel subsidies—but somehow they never get around to implementing them. The UN Environmental Program has identified ninety green goals that governments have established but notes that “significant progress” has been made on only four of them. “We live in an age of irresponsibility,” says UNEP executive director Achim Steiner.

As frustrating as it is to see the solutions ignored, it is also instructive. Environmental and development advocates often act as if the problem is a lack of information: give leaders more facts and they will make better decisions. But the world doesn’t work that way. Fighting climate change and poverty requires dismantling political and economic practices that are lucrative to powerful interests and replacing them with alternatives that serve the commonweal. No politician will take such steps lightly, for the powerful retaliate. The past twenty years demonstrate that appealing mainly to the conscience of world leaders does not work. Instead one must change those leaders’ political calculations—making them as afraid of an aroused public as they are of the narrow interests behind the status quo. There are various ways to do that, from voting politicians out of office to marching in the streets. But whatever form it takes, there is no substitute for mass political action if we hope to turn this sinking ship around in time.